1. Field of the Invention
The present invention relates to an electric junction box. Specifically, the electric junction box is configured for installation in an automobile and includes a power distributor (PD). The PD includes relays, as well as other electronic components, mounted on one side of a circuit board and bus bars fixed on the other side of the circuit board.
2. Description of Related Art
Conventionally, an electric junction box, such as those junction boxes for distributing electric power to each of the wire harnesses in an automobile, has a large number of relays and fuses, and a connector-connecting portion is formed on the outer surface of the box for connecting bus bar circuits to wire harnesses, the bus bar circuits being contained inside the electric junction box. In recent years, the number of electrical circuits in an automobile has increased in accordance with the sharp increase in the number of electronic components installed in an automobile, as the automobile becomes more and more sophisticated. Therefore, the number of relays mounted in an electric junction box for installation in an automobile has become larger, thereby forcing the electric junction box to become more dense, as well as larger.
In response to such situation, an electric junction box has been provided with a power distributor (PD) built therein. The PD includes semiconductor switching devices (FET) and mounting relays such as SMD relays mounted on a printed circuit board, and a heat sink fixed on the other side of the printed circuit board.
For example, in Japanese Laid Open Patent Publication No. 2001-319708, shown in FIG. 5 of the present application, electric junction box 1 is disclosed, which includes power distributor PD 2 and branch circuit block 5. In PD 2, semiconductor switching device (FET) 3 is mounted on a printed circuit board; a bus bar is fixed on the back-side of the printed circuit board; FET 3, which requires large electrical current, is connected to the bus bar; and heat sink 4 is attached to the bus bar. Branch circuit block 5 is made from the lamination of bus bars and insulation plates. On the lower surface of case 6 of electric junction box 1, connector housings 7 are provided for permitting insertion of connectors of wire harnesses (not shown) installed in a vehicle. On the upper surface of case 6, fuse housing 8 is provided. Connector housings 7 and fuse housing portion 8 are connected to branch circuit block 5.
However, as it stands now, PD 2 of electric junction box 1 is made by using single circuit board. Since PD 2 is laterally juxtaposed to branch circuit block 5 in a horizontal direction, electric junction box 1 is enlarged by an amount measured by the dimensions of PD 2. This causes a problem in that the installation space required for installing electric junction box 1 in a vehicle becomes large. Further, when PD 2 is laminated on the lower surface of branch circuit block 5 for the purpose of minimizing the horizontal area of electric junction box 1, it puts restrictions on locations for connector housings 7. Power input and output between a wire harness and PD 2 is done via branch circuit block 5 from connector housings 7. Therefore, when making a design for the arrangement of connectors for each destination, there is a problem that circuit wirings of PD 2 and branch circuit block 5 become complicated.
Further, since heat sink 4 is exposed only on the lower surface of case 6 for radiating outwardly the heat generated in PD 2, it is possible that, depending on the position of electric junction box 1 relative to other components in a vehicle, the heat radiation capability of electric junction box 1 is not sufficient.
The present invention is provided to address the above-described problems. That is, the present invention reduces the size, simplifies, and enhances the heat radiation capability of an electric junction box having PDs built in it.